function animate(obj,target, callback){
	clearInterval(obj.timerId);
	obj.timerId = setInterval(function(){
		var step = (target - obj.offsetTop) / 10;
		step = step > 0 ? Math.ceil(step) : Math.floor(step);
		if (obj.offsetTop=== target) {
			clearInterval(timerId);
			callback && callback();
		} else {
			obj.style.top = obj.offsetTop+ step + 'px';
		}
	},15);
};